1. Field of the Invention
The present invention relates to a technique for interpolating tones of a multi-tone image.
2. Description of the Related Art
As a kind of image processing using a computer, various tone conversion for a multi-tone image are performed. A tone jump is disadvantageously generated due to the tone conversion for a multi-tone image. The "tone jump" means a phenomenon that image levels of adjacent areas change stepwise to omit at least one image level between them. Such a tone jump will cause a pseudo line, which is observed with naked eyes. In other words, the image having a tone jump disadvantageously shows a undesirable line although its original image has no such lines.
Conventionally, when such a tone jump is present, it is alleviated by averaging pixel data around the tone jump area. However, the averaging process disadvantageously blurs the image.